For batteries or cells, particularly lithium ion cells, it is important to measure the conditions of the cells. Generally, this means that there is circuitry in place to look for particular fault conditions, such as overvoltage and undervoltage. As can be seen FIG. 1, an example of a conventional circuit 100 can be seen, which measures fault conditions for cells.
In FIG. 1, there are several cells BAT0 to BAT2 that are coupled in series with one another. In this circuit 100, overvoltage and undervoltage conditions are measured. To accomplish this, each cell BAT0 to BAT2 employs a comparator 106-0 to 106-2 to (respectively) measure the whether the cell BAT0 to BAT2 has entered an overvoltage condition (which is indicated by signals OV0 to OV2) and employs a comparator 108-0 to 108-2 to (respectively) measure the whether the cell BAT0 to BAT2 has entered an undervoltage condition (which is indicated by signals UV0 to UV2). The levels for overvoltage are set by bandgap circuits 102-0 to 102-2, and the levels for undervoltage are set by bandgap circuits 104-0 to 104-2.
There are, however, numerous drawbacks to circuit 100. First, because there is direct measurement of the voltage of cells BAT0 to BAT2, high voltage elements (i.e., transistors) are required. Second, numerous bandgap circuits 102-0 to 102-2 and 104-0-104-2 are used. Each of the high voltage elements and bandgap circuit 102-0 to 102-2 and 104-0-104-2 consume a great deal of area, increasing the production costs of integrated circuits that measure fault conditions for cells.
Some other conventional circuits are: Huang et al., “Current Mode Multiple Input Maximum Circuit for Fuzzy Logic Controllers,” Electronics Letters, Vol. 30, No. 24, pp. 1924-1925, 1994; and Huang et al., “Modular Current Mode Multiple Input Minimum Circuit for Fuzzy Logic Controllers” Electronics Letters, Vol. 32, No. 12, pp. 1067-1069, Jun. 1996.